1. Field of the Invention
The present invention generally relates to an imaging apparatus and an imaging system. In particular, the present invention relates to capturing an object image.
2. Description of the Related Art
In recent years, image sensors in which the number of pixels ranges from several million to ten million or more has been employed for digital still cameras whose primary usage is still image recording. These cameras are used not only to capture truly high definition still images, but also for recording of high definition still images, high-resolution moving images, or movie recording such as NTSC that are becoming important functions. Although all pixel signals are utilized in truly high definition images, for images that are high definition and below, pixel signals to be read out are thinned out or addition of pixel signals is performed to increase sensitivity.
Japanese Patent Application Laid-Open No. 9-247689 discloses an arrangement of thinning and reading out the same color by adding output signals from each pixel in units of 4×4 pixels. Japanese Patent Application Laid-Open No. 2001-36920 discloses an arrangement of adding a plurality of pixel signals employing 4×4 pixels as one component such that the spatial color array of each color before addition is the same as that of each color after addition.
Japanese Patent Application Laid-Open No. 9-046596 discloses an arrangement comprising a common amplifier in each pixel and performing an addition of pixels with a floating unit of the common amplifier.
According to Japanese Patent Application Laid-Open No. 9-247689, although thinning and addition is performed, addition is carried out using vertical signal lines and horizontal signal lines. As a result, a large amount of kTC noise is generated by parasitic capacitances of the signal lines, and enhancing SN is difficult. Further, according to Japanese Patent Application Laid-Open No. 9-247689, a plurality of pixels arranged in a matrix are grouped in components of 4×4 pixel units, and among the color signals of pixels arranged inside these components, four signals of the same color are added.
According to the arrangement disclosed in Japanese Patent Application Laid-Open No. 9-247689, since the optical sampling pitches of the pixels to be added, that is, the spatial centroids, are not substantially the same pitch in the horizontal direction and vertical direction, an extremely large moiré is created and the image quality deteriorates significantly.
According to an arrangement disclosed in Japanese Patent Application Laid-Open No. 2001-36920, although the number of pixel signals added within a single component is increased to enhance sensitivity, pixel rows are not thinned out and it is difficult to achieve high speed driving. In a pixel amplifier-type area sensor, driving is performed in which the pixel amplifier is reset in units of each pixel row, noise is read out, photoelectric conversion signals are transferred, and the photoelectric conversion signals are read out. This driving requires several μ seconds of time, and speeding up is thus not possible in sensors with a large number of pixel rows.
According to an arrangement disclosed in Japanese Patent Application Laid-Open No. 9-046596, a signal addition is performed with a floating unit and thus sensitivity is enhanced. However, similarly to Japanese Patent Application Laid-Open No. 2001-36920, the signals of all pixels are transferred to a floating unit and are also read from a pixel amplifier, and thus time is required for this driving and the operation cannot be carried out at the driving frequency of moving images.
As described above, with the prior art, even when thinning and pixel addition is performed, moiré is created since the spatial centroids of the pixels to be added are not substantially the same pitch. Further, there is a problem that even when addition of pixel signals is performed with a common pixel amplifier, time is required for pixel driving and a driving frequency of moving images cannot be obtained.